The invention relates to a method of operating a gaseous fuel internal combustion engine with a combustion air feed line which includes a compressor and a fuel supply line connected to the air feed line upstream of the compressor.
For the operation of modern internal combustion engines, gaseous fuels are also used in addition to the known liquid fuels in order to reduce consumption and emissions. Often, both, liquid and gaseous fuels are used at the same time, that is to say selectively, for bivalent operation.
When using gaseous fuels, in particular natural gas, a good mixture of the natural gas with combustion air is generally only conditionally obtainable because of the material properties of gaseous fuels, in particular at medium and high loads, due to displacement of the combustion air when large gas quantities are introduced which adversely affects mixing so that a desired gas/air mixture preparation is difficult to achieve. The conventional concepts for a gas operating mode often are based on an internal combustion engine operating on the gasoline or Diesel cycle, so that an optimized gas operating mode with good gas/air mixture preparation could only be realized to a limited extent.
DE 10008959 A1 discloses a gas engine in which, to obtain intensive mixing of the gas and the combustion air, a gas mixing device is provided in the form of a venturi mixer. Here, an axially displaceably mounted streamlined control element is arranged in a venturi pipe and, in addition, an insert consisting of a microporous material is inserted in the region of the narrowest point of the venturi pipe. The gas is fed into said micro-porous material via feed lines, and exits the micro-porous material for mixing in the narrowest region of the venturi pipe with the combustion air flowing through the pipe. The gas is admixed to the combustion air by means of a large-area mixing insert.
EP 1170490 A2 discloses a gas-operated internal combustion engine in which a turbocharger is arranged at the exhaust side and a compressor and a blow-off valve are arranged in the intake system. The air/gas mixture is prepared upstream of the compressor in an air/gas mixer and is compressed by the turbocharger. In the region of the blow-off valve, a pressure sensor is provided for detecting the mixture pressure providing a signal by which the mixture pressure is to be adapted as a function of load via a closed-loop control device by controlling the blow-off valve, in such a way that a loss of charge pressure is prevented during a load change. It has however been found that the concepts presented are not suitable for good mixture preparation.
It is an object of the present invention to provide a method in which improved mixture preparation is obtained using simple measures.